package com.example;

import com.gargoylesoftware.htmlunit.DefaultCredentialsProvider;

public class Main {
    public static void main(String[] args) {
            //...

            // set proxy username and password
            final DefaultCredentialsProvider credentialsProvider = (DefaultCredentialsProvider) webClient.getCredentialsProvider();
            credentialsProvider.addCredentials("username", "password");
    }
}